As a control for a vaccine challenge study, we have inoculated four monkeys with Mycobacterium tuberculosis strain H37Rv. Two monkeys received 10 million organisms and two received 20 organisms. The high dose monkeys developed clinical signs of dyspnea, coughing, anorexia, and weight loss 4-6 weeks after inoculation. Skin testing with Old tuberculin and PPD remained negative. Flow cytometry demonstrated increases in CD29+ and CD45RA+ subsets of CD4+ (helper-inducer and naive T cells) cells and decreases in CD16+ (NK) and B cells within two weeks of inoculation. Radiography indicated severe involvement of half the lung and bronchial nodes. Death of high-dose animals at 5 and 10 weeks was due to massive granulomatous inflammation of the inoculated half of the lung with spread to the bronchial lymph node but little evidence of inflammation outside the chest cavity. Low dose animals remained normal except for a positive skin test response to OT at 10 weeks. Characterization of this model continues.